As semiconductor devices scale to smaller dimensions, a need has arisen to more accurately define and control the dimensions and shapes of photoresist (resist) features used to pattern substrates. Conformal, uniform dielectric films have many applications in semiconductor manufacturing. In the fabrication of sub-micron integrated circuits (ICs) several layers of dielectric film are deposited. For example, four such layers are shallow trench isolation (STI), pre-metal dielectric (PMD), inter-metal dielectric (IMD) and interlayer dielectric (ILD). All four of these layers require silicon dioxide films filling features of various sizes and have uniform film thicknesses across the wafer.
Applications such as self-aligned doping may include a top part of an IC trench capped with a hardmask so just the bottom part of the fin is exposed to the dopant source. Another application may include a gap fill requiring bottom up film deposition to achieve void/seam free trench isolation.
Chemical vapor deposition (CVD) is one method for depositing silicon dioxide films. However, as design rules continue to shrink, the aspect ratios (depth to width) of features increase, and traditional CVD techniques can no longer provide void-free gap-fill in these high aspect ratio features. An alternative to CVD is atomic layer deposition (ALD). ALD methods involve self-limiting adsorption of reactant gases and can provide thin, conformal dielectric films within high aspect ratio features. An ALD-based dielectric deposition technique may involve adsorbing a metal containing precursor onto the substrate surface, then, in a second procedure, introducing a silicon oxide precursor gas.
However, current thin film deposition methods lack adequate control over where the deposition happens. For processes such as LPCVD (low pressure CVD) and ALD, the film deposition is conformal. LPCVD relies on thermal reaction on the surface, and ALD is a layer process through sequential chemical exposure. For plasma enhanced chemical vapor deposition (PECVD) processes, the deposition may result in a “bread-loaf” shape due to the ion-induced deposition.
In some approaches, ALD relies on alternate pulsing of the precursor gases onto the substrate surface and subsequent surface reaction of the precursors. ALD can also be achieved in a plasma environment (PEALD) as the surface is exposed to the active species generated by plasma during the reactant process. However, typical ALD chemistry is self-limiting with no areal selectivity, the areal selectivity giving conformal behavior of the deposition.
Furthermore, plasma ions affect film property modification, yet have minimal control over the surface reaction. For example, with PECVD, the film formation is mainly due to radical reaction on the surface, wherein controlling the reaction location to achieve directional ion beam deposition is difficult. In some prior art approaches, there exists a possibility to utilize directional ion bombardment toward higher deposition rate at a specific location. However, the impact is minimal due to the small ion/neutral ratio generated from the flow discharge.